Thrust reverser

ABSTRACT

A thrust reverser for a gas turbine engine ( 10 ) comprises cascade structures ( 20,22 ) mounted in an engine cowl ( 12 ). The cascades ( 20,22 ) comprise a plurality of air deflecting vanes ( 24 ) arranged in fixed space relationship. At least one of the cascades ( 22 ) translates between a first inoperative position where the cascade ( 22 ) is stowed radially inward of the cowl ( 12 ) and a second operative position where the cascade ( 22 ) is clear of the cowl ( 12 ) to expose the air deflecting vanes ( 24 ). When the trust reverser is operative blocker doors ( 26 ) pivot across an annular duct ( 13 ) defined between the core engine ( 11 ) and the cowl ( 12 ) to deflect the airflow passing therethrough to the exposed cascades ( 20,22 ) to produce a braking force.

The present invention relates to a thrust reverser for a gas turbineengine and in particular to a thrust reverser provided on a ducted fangas turbine engine.

Thrust reversers are used on gas turbine engines to reverse thedirection of the gas stream and thus use engine power as a decelerationforce. On ducted fan gas turbine engines, reverse thrust action isachieved by reversing the fan airflow. As the majority of thrust isderived from the fan sufficient reverse thrust is achieved by reversingthe cold fan stream airflow alone.

Thrust reversers on ducted fan gas turbine engines comprise a pluralityof doors which can be translated into a position in which they block thefan air outlet. The fan air is then deflected by the doors through aplurality of deflector vanes located in the engine cowling which areexposed by translation of the cowling. The fan air is directed in agenerally outward and partially forward direction by the deflector vanesto provide braking.

The deflector vanes are arranged in segments known as cascades which arepositioned around the circumference of the engine cowling. To achievesufficient braking the engine cowling must translate the length of thecascades to expose all the deflector vanes.

In ducted fan gas turbine engines the size of the cascades aredetermined by the amount of fan air that bypasses the core engine. Forhigh bypass ducted fan gas turbine engines the size of the cascades canlengthen the engine cowling considerably.

GB2182724B, which is owned by the applicant, provides cascades whichenable the length of the engine cowling to be shortened. In GB2182724Bthe vanes are stowed in a stacked relationship which reduces the overalllength of the cowling. in order for the deflector vanes to be stackedwhen stowed they are not securely mounted and the vanes may fail or bedamaged during operation of the thrust reverser.

The present invention seeks to provide a thrust reverser which iscompact when stowed to reduce the overall length of the cowling butwhich is less complex and in which the vanes are securely mounted toovercome the aforementioned problems.

According to the present invention a thrust reverser for a gas turbineengine includes a cowl and at least first and second cascade structures,each cascade structure comprising a plurality of air deflecting vanes infixed spaced relationship, the first cascade being fixed adjacent afixed portion of the cowl and the second cascade being mounted totranslate between a first inoperative position where the second cascadeis stowed radially inward of the first cascade and a second operativeposition where it is moved clear of the first cascade and the cowl toexpose the air deflecting vanes.

An annular portion of the cowl is translatable and the translatingcascade is preferably mounted on the translating portion of the cowl sothat movement of the cowl moves the cascade. The translating portion ofthe cowl may be intermediate the upstream and downstream ends of thecowl.

In the preferred embodiment of the present invention the cascadestructure is stowed within the fixed portion of the cowl in theinoperative position.

The thrust reverser may include blocker doors mounted for operation in agas duct, the outer wall of which is defined by said cowl, said blockerdoors being moveable between a position wherein they block the duct anddivert gases in the gas duct to the cascade and a position wherein theyprovide part of the flow structure of said duct outer wall.

The present invention will now be described with reference to theaccompanying drawings in which:

FIG. 1 is a diagrammatic view of a ducted fan gas turbine engineincorporating a thrust reverser in accordance with the presentinvention.

FIG. 2 is a sectioned side view a thrust reverser in accordance with thepresent invention in the stowed position.

FIG. 3 is a sectioned side view of the thrust reverser in accordancewith the present invention in the deployed position.

With reference to FIG. 1, a ducted fan gas turbine engine generallyindicated at 10 comprises a core engine 11 surrounded by an annular cowl12 to define an annular duct 13. The downstream portion 16 of the cowl12 is translatable relative to the remainder 14 of the cowl 12.Translation of the downstream portion 16 of the cowl 12 is brought aboutby the operation of rams 18 located in the fixed upstream portion 14 ofthe cowl 12.

A number of thrust reverser cascades 20, 22 are stowed within the cowl12, FIG. 2. Each cascade 20, 22 comprises a plurality of deflector vanes24 in fixed space relationship. The cascade 20 is attached to the fixedportion of the cowl 14. The cascade 22 is mounted on the translatableportion 16 of the cowl 12 so that it is stowed radially inward of thefixed cascade 20.

The translating portion 16 of cowl 12 comprises a portion intermediatethe upstream end of cowl 12 and the downstream end of cowl 12.

The translatable cowl portion 16 includes within its inner wall a numberof equiangular, spaced blocker doors 26. Each blocker door 26 ispivotable connected at its upstream end to the inner wall of the cowlportion 16.

When the thrust reverser is deployed, FIG. 3, the cowl portion 16translates rearwards. The blocker doors 26 pivot across the annular duct13 to a position where they block most or all of the duct 13 at aposition downstream of the cascades 20,22. The cascade 22 moves as thecowl portion 16 translates rearwards. The deflector vanes 24 in thecascade 22 are exposed and air deflected by the blocker doors 26 passesthrough the deflector vanes 24 to produce a braking force.

It will be appreciated by one skilled in the art that the thrustreverser may have any number or different combinations of fixed andtranslatable cascades 20,22. The mechanism for translating the cascades22 from the stowed inoperative position to the operative position may beindependent or connected to the mechanism for translating the cowlportion 16.

I claim:
 1. A thrust reverser for a gas turbine engine including a cowland at least first and second cascade structures, each cascade structurecomprising a plurality of air deflecting vanes in a fixed spacedrelationship, the first cascade being fixed adjacent a fixed e portionof the cowl and the second cascade being mounted to translate between afirst inoperative position where the second cascade is stowed radiallyinward of the first cascade and a second operative position where thesecond cascade is translated downstream of the first cascade to aposition where the air deflecting vanes are exposed.
 2. A thrustreverser as claimed in claim 1 in which an annular portion of the cowlis translatable relative to a fixed portion thereof.
 3. A thrustreverser as claimed in claim 2 in which the second cascade is mounted onthe translating portion of the cowl so that movement of the cowl movesthe cascade.
 4. A thrust reverser as claimed in claim 1, in which thesecond cascade when inoperative is stowed within the translating cowlportion.
 5. A thrust reverser as claimed in claim 2 in which thetranslating portion of the cowl comprises a portion intermediate theupstream and downstream ends of the cowl.
 6. A thrust reverser asclaimed in claim 1 including blocker doors mounted for operation in agas duct, the outer wall of said gas duct being defined by said cowl,said blocker doors being moveable between a position wherein saidblocker doors block the duct and divert gases in the gas duct to thecascade and a position wherein they comprise part of the flow structureof said duct outer wall.
 7. A thrust reverser as claimed in claim 3 inwhich the translating portion of the cowl comprises a portionintermediate the upstream and downstream ends of the cowl.